Evidence for pitch angle diffusion of solar wind protons in resonance with cyclotron waves

被引:104
作者
Marsch, E [1 ]
Tu, CY
机构
[1] Max Planck Inst Aeron, D-37191 Katlenburg Duhm, Germany
[2] Peking Univ, Dept Geophys, Beijing 100871, Peoples R China
[3] Peking Univ, State Key Lab Turbulence Res, Beijing 100871, Peoples R China
关键词
D O I
10.1029/2000JA000414
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Quasi-linear theory predicts that ions in resonance with transverse ion cyclotron waves suffer merely pitch angle diffusion while conserving their total kinetic energy in the frame moving with the wave phase speed. For the first timer direct observational evidence from Hellos plasma data is shown for the occurrence of this pitch angle diffusion of solar wind protons, induced by resonance with parallel ion cyclotron waves propagating away from the Sun. Parts of the isodensity contours in velocity space are well outlined by a sequence of segments of circles centered at the adapted wave phase speed, which is ass;med to vary slightly and to be due to dispersion smaller than the local Alfven speed. This observation confirms the validity of basic concepts of resonant wave-particle interactions as described by quasi-linear theory. The solar wind proton velocity distributions show a "plateau" defined by a vanishing pitch angle gradient in the resonant regime, implying marginal stability of the distribution function. The implications of these results for solar wind ion heating and kinetic transport are discussed.
引用
收藏
页码:8357 / 8361
页数:5
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